Fix allocator + serialization (#481)

Author: GPeaky

lessons/257/actix-app/Cargo.lock

@@ -5,6 +5,7 @@ edition = "2024"
 
 [dependencies]
 actix-web = "4"
+mimalloc = { version = "0.1.48", default-features = false }
 serde = { version = "1", features = ["derive"] }
 
 [profile.release]

lessons/257/actix-app/Cargo.toml

@@ -3,6 +3,9 @@ mod routes;
 
 use actix_web::{App, HttpServer, web};
 
+#[global_allocator]
+static GLOBAL: mimalloc::MiMalloc = mimalloc::MiMalloc;
+
 const PORT: u16 = 8080;
 const THREADS: usize = 2;
 const API_PATH: &'static str = "/api/v3/ticker/bookTicker";